The goal of this Program Project is to understand the cellular and molecular mechanisms of transplantation tolerance, both generally and in particular as they apply to the cure of diabetes by islet transplantation. Tolerance is the process that limits the degree to which lymphocytes respond to self antigens. Failure to acquire tolerance is the cause of autoimmune diseases. Inability to induce it prevents us from curing those diseases by organ transplantation. To understand tolerance and how to induce it, four Projects will study the cellular and molecular components of transplantation tolerance and will test their findings in the living diabetic animal. Project #1 will exploit a new mouse system based on "synchimeras" to identify the cellular mechanisms of allograft tolerance induction and maintenance Project #2 will use synchimeras in a new model system based on the NOD mouse to identify the mechanisms underlying their resistance to transplantation tolerance induced by costimulation blockade. The project will distinguish these mechanisms from those underlying the loss of selftolerance and expression of autoimmunity. Project #4 will investigate the molecular basis of anergy, one of the leading candidate mechanisms for the induction and maintenance of tolerance. The PI has generated a database of genes up-regulated or down-regulated upon induction of T cell anergy and will focus on two exciting candidate genes, PAC-1 and Egr2. Project #5 will test the hypothesis that T cells recognizing their specific antigen together with a death-inducing molecule on a professional antigen presenting cell will be selectively eliminated. This will be done by engineering professional antigen presenting cells to express death-inducing molecules and then using these transduced cells to tolerize animals. In support of these projects, Islet Isolation and Transplantation and Animal Core Units are proposed. Building on consistent progress made during two previous funding periods, our immediate goal is to gain new molecular and cellular understanding of tolerance in vitro and in animal models. Our ultimate goal is to translate our findings into methods for curing diabetes mellitus in both adults and children.